The present invention relates to an electric refrigerator and, more particularly, to a temperature control apparatus for controlling the supply of a refrigerant to coolers individually disposed in a refrigeration chamber and a freezer.
In general, in electric refrigerators each having coolers individually disposed in a refrigeration chamber and a freezer (i.e., a so-called "two-temperature type" refrigerator), the cooler for the refrigeration chamber is provided in the rear upper portion thereof. An electronic circuit controls the supply of a refrigerant to the cooler in the refrigerator of this type in the following manner. When the temperature of the cooler itself, which is detected by a temperature sensor, rises to a preset upper limit reference temperature, a temporary memory element such as a flip-flop is set to supply the refrigerant to the cooler, thereby cooling the inside of the refrigeration chamber. Another temperature sensor is arranged in the refrigeration chamber so as to detect the chamber temperature. When the chamber temperature detected by this temperature sensor drops below a preset lower limit reference temperature, the temporary memory element is reset to stop supplying the refrigerant. Temperature control is thus performed such that the refrigerator temperature lies within a range for proper food storage.
However, when the user frequently opens/closes the refrigerator door to place food therein or take it out therefrom, or when the refrigerator door is left or kept open, the temperature cannot be properly controlled even if the cooler is properly operated. The temperature of air around the sensor therefore cannot be properly lowered. As a result, the refrigerant continues to be supplied to the cooler, and the cooler becomes overloaded. A thick frost layer is deposited on the surface of the cooler, resulting in inconvenience.
Furthermore, conventionally, the logic level of the temporary memory element may change due to noise generated when the compressor or a solenoid operated valve for switching a refrigerant flow is turned on/off. Thus, refrigerant cannot be properly supplied due to erroneous operation of the temporary memory element. In order to prevent this erroneous operation, a plurality of special protective circuits are required, resulting in high cost.
A large freezer has been recently furnished in a refrigerator along with the development of "home freezing". In order to cool the freezer so as to freeze food stored in the freezer, the temperature of the surface of the freezer cooler is kept at -40.degree. C. For this reason, in the conventional refrigerator where the ON-OFF operation of the compressor is controlled with reference to the freezer temperature, a time interval after the compressor is turned off and before it is turned on again is prolonged. If the user frequently opens/closes the refrigerator door, the compressor may not be turned on even if a thermistor for detecting the chamber temperature generates a refrigeration selection signal. As a result, the refrigerator temperature rises, resulting in undesirable effects on food stored therein.